In recent years, it has been firmly established that multigene families are a ubiquitous and important feature in the genomes of higher eucaryotes. Gene families are especially important since they often encode complex aspects of differentiated cell phenotypes and may play key roles in developmental and physiological regulation. Gene families are also important because they reveal the processes that both diversify eucaryotic genomes and maintain certain genetic features relatively invariant--including sequence elements that may be involved in developmental regulation. We are studying that evolution of structural gene families and of the regulatory elements controlling their developmental expression, using as a model system the silkmoth chorion multigene families. We want to document how the structural genes in these families have evolved, by localized fixation of mutations (subtitutions and deletions/duplications) as well as by gene conversion. Furthermore, we want to compare and contrast the evolution of the structural chorion genes with the evolution of non-transcribed sequences that may be involved in the regulation of gene expression. The fundamental approach here is to define precisely families, and to relate it to the sequence features of these genes and their immediately flanking DNA. Finally, we wish to pursue our analysis of the morphogenesis of the complex chorion structure, by taking advantage of variations established during evolution as well as studying some newly discovered chorion mutants in Bombyx mori.